The present invention relates to circuits for a switching mode driving of a load and in particular to circuit arrangements for controlling the current being delivered to the load.
Apparatuses for controlling electric motors and more generally for delivering a current to inductive loads utilize the so-called Pulse Width Modulation technique (PWM). This technique is implemented by means of an "H-bridge" stage utilizing a square-wave driving signal, whose frequency and duty-cycle are controlled by means of a clock signal, and the inverted signal thereof which are applied, respectively, to two pairs of switches arranged in a bridge configuration and operatively switching the load between a supply and a ground or a virtual ground node of the bridge stage. For implementing a system for monitoring and controlling the current being delivered to the load, sensing resistances, connected between the virtual ground nodes of the two branches of the H-bridge stage and the real ground of the circuit are frequently used. These sensing resistors must necessarily be power components, suitable to withstand the current which flows through the load, and for this reason are almost exclusively discrete components, connected externally to an integrated driver circuit and generally representing a remarkable cost factor of the apparatus also because they must often possess well determined precision and temperature coefficient characteristics and be exempt of any appreciable inductance.
The circuit for sensing the magnitude and direction of the current according to the present invention determines the magnitude and direction of the current being delivered to a load of an H-bridge stage by utilizing a single sensing resistor connected between a common virtual ground node of the driving bridge circuit and a real ground node.
The different aspects and advantages of the invention in relation to the known technique will be more easily understood through the following description with reference to a series of drawings, wherein: